在选择中添加带有“ *”的额外列

Question

I am writing a query sql for a data migration job to fetch data and send from mysql-server a to mysql-server b.

Server a has different databases, representing different game channel, and each database has a table tablex , they have same table name and same schema:

 uid  level
 123    3
 211    5

While in server b there is only one table tablex to receive tablex of all databases and it has one more column - channel

channel uid  level
 1      123    3
 1      211    5
 2      355    2

I can parse channel number from db name via python but I need to put this constant in the sql and since there are many tables, I cannot fix the columns. So just want to make sure is there any way to do this like:

select 1,* from xxx.yyy

Answer 1

You could try adding alias and table name

select 1 as my_col, yyy.* from xxx.yyy

or using string

select cast('1'  as  unsigned) , yyy.* from xxx.yyy

Answer 2

Yes, you can wrap the query into another SELECT and add the columns, eg:

SELECT A.*, '1'
FROM (
  SELECT *
  FROM your_table
) A;